The invention relates to a method and a grinding machine for controlling the process during traverse grinding of a workpiece wherein real-time control is effected.
High accuracies are already achieved with the grinding methods known and used today and with the grinding machines working with these methods. In accordance with a general tendency during manufacture of components in a production process, both monitoring of the process and specific control of the process are necessary in order to reduce a defect rate. If need be, corrective action is already taken during the actual grinding operation in order to achieve a uniformly good quality of the workpiece to be manufactured.
In plunge-cut grinding and swing-frame grinding, in-process-measuring and process-control devices for controlling grinding processes are known. In peripheral traverse grinding, which is also designated as rough grinding, a genuine in-process measuring and process control has hitherto not been realizable because an outside diameter, to be produced during travers grinding, is ground with a traverse stroke and therefore no substantial intermediate steps are recorded via a measuring control in order to then be able to still influence a final value.
During the peripheral traverse grinding process, work has therefore been carried out hitherto only according to the xe2x80x9cpost-process-measuring and process-control method.xe2x80x9d This has the disadvantage that the outside diameter already ground, e.g. a fitting seat, can no longer be subsequently corrected on the workpiece being machined if the actual size has already been ground to undersize.
The object of the invention is therefore to provide a method and a grinding machine, by means of which, during traverse grinding, a diameter can be continuously corrected to a desired diameter to be ground in a reliable manner, which method and grinding machine can be used industrially and in which the measuring method used for in-process-measuring and process-control method or the measuring device used for it require no extension of machining.
The method according to the invention constitutes a method of controlling traverse grinding of a workpiece by means of a grinding wheel on a grinding machine such that a workpiece, during the grinding, is constantly or continuously measured by means of a measuring sensor to determine an existing actual size, and parallel thereto, i.e. simultaneously, the measured actual size is used to automatically and continuously correct grinding to grind the workpiece to a preset grinding-time-dependent desired size. The actual size is corrected to the desired size on the basis of the measured actual size in real-time control of the grinding machine, i.e. in an in-process control. Such a real-time control avoids a situation in which the workpiece to be ground is ground to undersize. As a result, the defect rate during the manufacture of the workpieces can be considerably reduced. Furthermore, the grinding operation can be actively influenced by the real-time control in such a way that heat input introduced into the workpiece by the grinding wheel is reduced or optimized, as a result of which, on the one hand, deformations at the workpiece which are caused by heat and which may likewise lead to inaccuracies of the actual sizes of the workpiece can be reduced, and at the same time the grinding-wheel wear can also be reduced. Optimum grinding conditions can thereby be achieved overall.
The desired size is preferably preset as a time-dependent desired-value curve. In this case, the time-dependent desired-value curve is filed in a storage unit which is preferably an integral part of the machine control. In accordance with the desired-value curve, a correction is then carried out after constant or continuous determination of the respective actual value, so that the grinding wheel approaches the desired-value curve as a function of the grinding time in such a way that the desired final contour on the workpiece is achieved.
In an embodiment of the invention, the actual size is measured directly in a region of engagement of the grinding wheel on the workpiece. The expression xe2x80x9cdirectly in a region of engagement of the grinding wheelxe2x80x9d is intended to refer to the fact that a measuring sensor, emitting a measured value in the form of a measuring signal, is arranged essentially in a plane which is defined by an engagement point locus on the rotating workpiece of the grinding wheel. This advantageously achieves the effect that the measurement is effected directly at that point on the workpiece at which the workpiece is just being ground, so that, in the event of the slightest deviations from the desired-value curve, a correction in the direction of the desired-value curve can be carried out immediately via the machine control in order to avoid an undersize cut.
The continuously measured actual size is preferably transmitted as a measuring signal to a machine controller, the correction to the desired size then being effected on the basis of this measuring signal. This corresponds to a real-time control, which is also designated as in-process control. According to the invention, a method in which an in-process control is realized during rough grinding is therefore provided. In accordance with this method according to the invention, the grinding wheel is subsequently corrected to a desired diameter of the workpiece during the grinding.
In accordance with a certain workpiece contour to be ground, the workpiece is ground cylindrically or in a tapered manner at least in one section. That is to say that it is possible, with the method described, to grind both cylindrical and tapered workpieces at their outer contour to a defined desired-value curve with the greatest accuracy.
In order to ensure that the recording of the measured value, on the basis of which the real-time control is effected, always takes place in the region of engagement of the grinding wheel or in the plane formed by the engagement point, rotating on the workpiece, of the grinding wheel, the grinding wheel and measuring sensor are moved in synchronism with one another at the workpiece. In a corresponding manner, it is of course also possible for the grinding wheel and measuring sensor to be fixed and for the workpiece to be moved instead. In this case, too, it is ensured that the grinding wheel and measuring sensor are arranged relative to one another in such a way that the recording of the measured value relates to that point on the workpiece at which the grinding operation is directly taking place. In the method according to the invention, it is not necessary to switch off the machine for the purpose of the measuring operation or to remove the grinding wheel from the workpiece for carrying out the measuring operation.
According to a further aspect of the invention, the grinding machine according to the invention, which serves in particular to carry out the method described above, has a grinding wheel held on a wheelhead and intended for traverse grinding of a workpiece held between a work spindle and a tailstock quill, a measuring sensor for recording a workpiece dimension which has just been ground, and a machine controller. According to the invention, the measuring sensor is arranged essentially in a plane defined by an engagement region on the rotating workpiece, of the grinding wheel, in which case measuring signals can be fed continuously to the machine controller during the traverse grinding. The machine controller in turn, on the basis of these measuring signals, controls the grinding wheel in such a way that the grinding operation can be carried out with real-time control. With the device according to the invention, it is therefore possible to influence the manner of the engagement of the grinding wheel on the workpiece directly during the grinding operation without a time delay, i.e. in real-time control, in such a way that the desired final sizes of the workpiece can be kept within the narrowest possible tolerance range, so that an undersize cut of the workpiece, which as a rule is unacceptable, can be avoided.
In an embodiment of the invention, the measuring sensor is fastened to a measuring head which is attached to the wheelhead in such a way that it can be swung in. Due to the measuring head being attached in such a way that it can be swung in, it can be adapted to various diameters of the workpiece, it always being ensured that the measuring sensor is arranged on the measuring head in such a way that it is always located in the region of the plane defined by the present engagement points of the grinding wheel on the workpiece. According to a preferred embodiment of the invention, the measuring sensor is arranged opposite the engagement region of the grinding wheel on the workpiece, i.e. preferably essentially 180xc2x0 opposite the engagement region of the grinding wheel. However, it is also possible to arrange the measuring sensor at a certain angular distance at the periphery of the workpiece. With the real-time process control according to the invention, in combination with the machine control on the basis of the recorded actual values, which are used to correct the desired values, it is possible to produce a desired cylindrical form or a desired tapered form of the workpiece. This means that the traverse grinding according to the invention can be used both for cylindrical workpiece forms or workpiece sections and for tapered workpieces or workpiece sections.